1. Field of the Invention
The present invention relates to a master-slave card system and method for operating the same, especially to a master-slave card system using polling scheme to convey command to the slave cards and method for operating the same.
2. Description of Prior Art
The conventional master-slave card system utilizes interconnected digital input and output points (DI/O) for communicating signals among master card and slave card. A related-art master-slave card system integrates all of the digital input and output points (DI/O) on a single circuit board. However, it could induce a mess if lots of digital input and output points (DI/O) are provided on the same circuit board. Moreover, the layout of the digital input and output points (DI/O) is predetermined in the beginning of manufacture of the circuit board. Therefore, the number of the digital input and output points (DI/O) may be excessive and cost is increased. Alternatively, the number of the digital input and output points (DI/O) may be insufficient and it is inconvenient for user. Another related-art master-slave card system utilizes serial communication for the I/O control of the digital input and output points (DI/O) and a half-duplex scheme is used for the communication therebetween. In the half-duplex scheme, the master card and slave card cannot send their signal to each other simultaneously. Therefore, unwanted delay occurs and the signal cannot be transmitted in real time manner.
Therefore, it is desirable to provide a more flexible connection of remote digital input and output points (DI/O) for a local master card.